Position measurement of a stepping motor

Abstract

A method for measuring the position of a stepping motor by generating a signal representative of the back electromotive force induced by the rotor in the coils of the motor, and estimating the actual position of the rotor from the signal representative of the back electromotive force induced by the rotor.

We claim: 
     
       1. Apparatus for position measurement of a stepping motor having a rotor and a plurality of electromagnetic field windings adapted to be separately energized to control rotation of said rotor comprising: means for generating signals representative of a back electromotive force induced by said rotor in the field windings, the means for generating including   means for indirect measurement of a field winding voltage through low-pass filtering of switching control logic of a full bridge amplifier and   means for removal of a voltage contribution of the resistance and inductance of said field windings from the field winding voltage measurement, and   means for estimating said roto position using the signals representative of the back electromotive force of said field windings.   
     
     
       2. The apparatus for position measurement of claim 1 including means for estimating and correcting steady state phase error introduced by said low pass filtering.